Fuelly Forums - Alternator v. no alternator

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Good link, clencher. You're the link man for sure.

The thing I keep coming back to is only the 15% loss on the alternator. I find it really hard to believe that an alternator can turn 85% of the mechanical power in to electrical energy. Maybe they do, but it seems really high to me. Heck a switching inverter is lucky to be 90% efficient with no moving parts. And a DC motor attached to an AC motor is also only about 50% efficient. So how the heck can an alternator be more efficient then a motor inverter? I would think an alternator is about 50% efficient at the top end. Maybe I am all wet, but this just doesn’t sit right with me.

It also wouldn't explain the larger gains we are seeing by disabling them. 100w or less then 1/4 HP should mean a 10% increase in mileage HP wise. Maybe they are 85% efficient at 50% loading and only 25% efficient at 10% or normal loading?

Numbers I get from eCycle is that the alternator is about 60% efficient but again at what load. They have a pretty free spinning rotor even when magnitized and slip ring brushes so not much loss there so you get into I2R losses at high currents and the diode drops all the time. It really comes down to how much current the car draws constantly . . . 20 amps at 14 volts is 280 watts doubled for 50% efficiency is still only 560 watts . . . add some belt and fan losses in the alternator and you get less than 1 HP. If you like I can run an alternator on an electric motor and tell you how many watts it takes - all I need is a belt and pulley for the motor.

Sounds like way to much work but I would be curious to know what it really takes to drive the alt.

It's funny you mention that because one of my first thoughts was to drive the alternator in my car off a 1 hp DC motor from the spare battery. Seemed like an evil circle and I thought the losses would be less to go the inverter/charger route. It also allows me to very easily re-connect the alternator for trips or if my wife takes the car.

Posting this message on behalf of John David Shelton, who is the founder/moderator of the MaxMPG Yahoo group: https://autos.groups.yahoo.com/group/maxmpg/

John David is currently serving in Iraq. He has limited bandwidth (thus the request to post this for him).

EDIT: his personal web site: https://maxmpg.org/

Feel free to reply to his thoughts on alternators / charging (prompted by this thread and my write-up at metrompg.com). He periodically reads stuff here at GS.

Quote:

Originally Posted by John David Shelton

Do you know of any alternators that are built to be more efficient? Do any of the hybrids have them and if so are they more efficient? What about a DC motor that puts out 14V, would that be a more efficient solution? I read once about a companythat was making a mild hybrid kit with a DC motor in place of the alternator along with a controller and battery or capacitor pack. It would help turn the drive train while also providing DC power.
How about using a clutch sort of like what air conditioner compressors use? That way you could get nearly the same benefits as no alternator connected but the option is there to switch it on. It would probably f reewheel easier than simply turning off the power to the alternator so it doesn't see any load.

I really like the idea of a thermocoupler. You might not get the same amount of power as with an alternator but you could possibly leave the alternator on the vehicle with a kill switch and just use it when the thermocouples can't keep up. Or, install a tiny 35 amp alternator such as was discussed in the thread to be augmented by the thermocouples. When I get back from Iraq, I'm going to look into figuring out how to build something like that. Since I've becom e interested in efficiency I've wanted to try and figure out a way to capture or use the heat energy lost in the exhaust. It's such a waste.

Concerning the turbo alternator, is it possible to put it anywhere on an exhaust? Does a turbo have to be on the manifold? Turbos spin a lot faster than an alternator, how difficult would it be to control the ra te at which a turbo spins an alternator? In a turbo alternator, would an experimentor simply build a fan on the alternator to be spun by the compressed air coming from the turbo or would it need to directly coupled somehow?

The electric water pump is something I'm going to try as soon as I can afford it, along with an electric power steering pump. There are off the shelf systems available for the water pump. The power steering migh t be more difficult. I'd prefer to go with manual steering but it looks as though my truck never had manual steering available as an option and I haven't been able to determine if the Nissan Pathfinder manual steering gear would drop in to my truck.&nbs p;The MR2 has a 12v steering pump and quite a few EVers have used this in their conversions.

And one last thought about batteries. In nearly every make and model of car, no matter what options are installed, the batteries are the same size, usually the same model of battery for every car. My truck, a st ripped down 1998 Nissan Frontier, has the same battery as the truck with all the options. So do I have more battery than I need? If true, make you think how many cars out there have too much battery and are needlessly wasting fuel chargin g batteries that are too big? Is it possible to run a vehicle, especially a small vehicle like a metro, off of a motorcycle sized battery? It would save weight and reduce charging requirements. Also, with a smaller battery it could be more easily r elocated to someplace else on the vehicle to give it a lower center of gravity to help a driver carry more speed through a corner allowing him to brake less. It's a minor amount, but I suppose every bit counts. I'm considering moving my battery to the f rame rails

If anybody has any suggestions for these ideas, please share them with the group.

Quote:

Originally Posted by Brock

The thing I keep coming back to is only the 15% loss on the alternator.

I've read figures ranging anywhere from 60% - 90% efficiency. Wikipedia states 90% efficiency for modern alternators (without any further information).

I'll take a stab at a couple of John David's points...

Quote:

Originally Posted by John David Shelton

Do you know of any alternators that are built to be more efficient? Do any of the hybrids have them and if so are they more efficient?

As far as I know, they don't have conventional alternators. The Toyotas and Hondas use DC-DC converters to step down the hybrid pack from high voltage to 13.5 (or whatever). I'm not sure if that's ultimately more efficient than running an alternator, since the gasoline engine ultimately does most of the recharging of the hybrid pack (with regen kicking in some as well).

Quote:

How about using a clutch sort of like what air conditioner compressors use?

To figure out if that would work, you'd need to know how much power the electromagnetic clutch draws in order to be engaged.

You know I was just thinking if we knew the amount of watt hours that we would need to operate for a desired time how about using a higher voltage NiMh or NiCad pack and regulate it to 14 volts out - I have some cheep 20-60 volts input 15 volts out (adjustable) - switching regulator modules 80% efficient and since the NiMh battery can be cycled a lot more than an SLA that could supliment the cars 12 volt battery and you could run a 12 volt to high voltage charger to recharge when going down long hills or slowing down although that recharge time would be minimum - solar or grid recharge would be easy enough at higher voltage.

Quote:

Originally Posted by John David Shelton

If true, make you think how many cars out there have too much battery and are needlessly wasting fuel charging batteries that are too big? Is it possible to run a vehicle, especially a small vehicle like a metro, off of a motorcycle sized battery?

I have a downsized battery in my Laser. Originally it called for a 525CCA battery which weighed 35 pounds. I got a smaller 420CCA battery that weighs 28 pounds. Not a huge weight savings, but I needed a battery at the time, so I thought, why not get something lighter? My other car has a 13 pound deep cycle battery rated at 330CCA. Works fine, no problem starting it when cold.

Would a larger battery require more amps to recharge it if the ammount of discharge to start it is the same?

Diesels vs. Gassers

Unfortunately, gassers need ignition/spark to operate, whereas a Diesel doesn't need a battery once running. This and the electrical systems such as power steering on newer cars would require quite the load.

If you know your maximum commuting distance, adjust it for temperature, and perform the calcs, I'm sure a zero-alternator/plug-in system could be implemented. The cost/weight is up to the experts...

RH77